1. Field of the Invention
This invention relates to a load drive circuit which supplies a drive load with an input signal inputted from outside. For example, the invention relates to the load drive circuit which is able to applied to a signal line drive circuit of a liquid crystal display integral with a drive circuit.
2. Description of the Related Background Art
A liquid display device is made up of a pixel array portion with a matrix arrangement of signal lines and scanning lines, and drive circuits for driving the signal lines and the scanning lines. Conventionally, since the pixel array portion and the drive circuits were formed on separate substrates, it was difficult to reduce the costs of the liquid display device, and it was also difficult to increase the ratio of the real screen size relative to the outer dimensions of the liquid crystal display device.
Recently, since the manufacturing technology for making TFT (thin film transistor) on a glass substrate by using polysilicon as its material has been progressed, it has been made possible to make the pixel array portion and the drive circuits on a common glass substrate by using this technology.
However, at present since making uniform property polysilicon TFTs on a grass substrate is still difficult, the threshold voltage and mobility thereof vary. Therefore, even if the pixel array portion and the drive circuit are formed on a common substrate, there is still a possibility that the variation in property of TFTs causes a deterioration of the display quality such as inconsistency in luminance. Furthermore, the power consumption increases as well.
The invention has been made taking these points into consideration, and its object lies in providing a load drive circuit preventing fluctuations of a voltage supplied to a driven load due to an influence of unevenness of the transistor property or the minimizing influence even if the voltage is influenced by the unevenness.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, a load drive circuit supplied with an input signal having a predetermined voltage amplitude and supplying a signal line connected with a load with the voltage of the input signal, comprising:
a signal line voltage control circuit, a first terminal of which is connected to the signal line, configured to control the voltage of the signal line so as to rise the voltage of the signal line when the voltage of the signal line is lower than that of the input signal and drop the voltage of the signal line when the voltage of the signal line is higher than that of the input signal, the signal line voltage control circuit including an odd number of inverters connected in series and setting each input terminal of the inverters at each threshold voltage of the inverters;
a first differential voltage holding circuit, a first terminal of which is connected to a second terminal of the signal line voltage control circuit and a second terminal of which is connected to an input terminal of the input signal when the input signal is supplied and connected to the signal line when the signal line voltage control circuit controls the voltage of the signal line, the first differential voltage holding circuit holding a differential voltage between the threshold voltage of the inverter positioned nearest to the input side of the signal line voltage control circuit and the voltage of the input signal when the signal line voltage control circuit controls the voltage of the signal line; and
a first differential voltage setting circuit configured to set the first differential voltage holding circuit at the differential voltage to be held in the first differential voltage holding circuit before the signal line voltage control circuit controls the voltage of the signal line.
According to another aspect of the present invention, a liquid crystal display device comprising:
a pixel array portion formed on a substrate, having signal lines and scanning lines aligned in longitudinal and transverse directions and having pixel electrodes near respective nodes of the lines; and
a drive circuit formed on the substrate to drive driving lines which are the signal lines and/or the scanning lines,
wherein the drive circuit includes at least one load drive circuit supplied with an input signal having a predetermined voltage amplitude and supplying the driving line with the voltage of the input signal, the load drive circuit comprising:
a driving line voltage control circuit, a first terminal of which is connected to the driving line, configured to control the voltage of the driving line so as to rise the voltage of the driving line when the voltage of the driving line is lower than that of the input signal and drop the voltage of the driving line when the voltage of the driving line is higher than that of the input signal, the driving line voltage control circuit including an odd number of inverters connected in series and setting each terminal of the inverters at each threshold voltage of the inverters;
a first differential voltage holding circuit, a first terminal of which is connected to a second terminal of the driving line voltage control circuit and a second terminal of which is connected to an input terminal of the input signal when the input signal is supplied and connected to the driving line when the driving line voltage control circuit controls the voltage of the driving line, the first differential voltage holding circuit holding a differential voltage between the threshold voltage of the inverter positioned nearest to the input side of the driving line voltage control circuit and the voltage of the input signal when the driving line voltage control circuit controls the voltage of the driving line; and
a first differential voltage setting circuit configured to set the first differential voltage holding circuit at the differential voltage to be held in the first differential voltage holding circuit before the driving line voltage control circuit controls the voltage of the driving line.
According to a further aspect of the present invention, a load drive circuit supplied with an input signal having a predetermined voltage amplitude and supplying a signal line connected with a load with the voltage of the input signal, comprising:
an inverting amplifier circuit, an output terminal of which is connected to the signal line when the inverting amplifier circuit controls the voltage of the signal line, including an odd number of threshold voltage setting inverter circuits connected in series, each of the threshold voltage setting inverter circuits having an inverter, a switch connecting between an input terminal and an output terminal of the inverter before the inverting amplifier circuit controls the voltage of the signal line, and a first capacitor connected to the input terminal of the inverter;
a second capacitor, one end of which is connected to an input side of the inverting amplifier circuit, and the other end of which is connected to an input terminal of the input signal when the input signal is supplied and connected to the signal line when the inverting amplifier circuit controls the voltage of the signal line; and
a constant voltage supplying circuit connected to the one end of the second capacitor and configured to supply a given voltage when a differential voltage to be held in the second capacitor during the inverting amplifier circuit controlling the voltage of the signal line is set in the second capacitor.
According to a still further aspect of the present invention, a load drive circuit supplied with an input signal having a predetermined voltage amplitude and supplying a signal line connected with a load with the voltage of the input signal, comprising:
an inverting amplifier circuit, an output terminal of which is connected to the signal line when the inverting amplifier circuit controls the signal line, including:
a first threshold voltage setting inverter circuit positioned nearest to the input side of the inverting amplifier circuit, and having an inverter and a switch temporarily connecting between an input terminal and an output terminal of the inverter before the inverting amplifier circuit controls the voltage of the signal line; and
an even number of second threshold voltage setting inverter circuits connected in series, each of the second threshold voltage setting inverter circuits having an inverter, a switch temporarily connecting between an input terminal and an output terminal of the inverter before the inverting amplifier circuit controls the voltage of the signal line and a first capacitor connected to the input terminal of the inverter; and
a second capacitor, one end of which is connected to the input terminal of the first threshold voltage setting inverter circuit, and the other end of which is connected to an input terminal of the input signal when the input signal is supplied and connected to the signal line when the inverting amplifier circuit controls the voltage of the signal line.
According to another aspect of the present invention, a load drive circuit supplied with an input signal having a voltage amplitude and supplying a signal line connected a load with the voltage of the input signal, comprising.
a differential amplifier circuit having an inverting input terminal, a non-inverting input terminal supplied with a reference voltage and an output terminal connected to the signal line;
a differential voltage holding circuit connected to the inverting input terminal of the differential amplifier circuit and configured to hold a differential voltage between the voltage of the input signal and the reference voltage; and
a first feedback circuit configured to supply the voltage of the input signal to the signal line while a feedback loop including the differential voltage holding circuit is constituted by connecting between the output terminal of the differential amplifier circuit and the differential voltage holding circuit with the differential voltage holding circuit holding the differential voltage.
According to a further aspect of the present invention, a liquid crystal display device comprising:
a pixel array portion formed on a substrate, having signal lines and scanning lines aligned in longitudinal and transverse directions and having pixel electrodes near respective nodes of the lines; and
a drive circuit formed on the substrate to drive driving lines which are the signal lines and/or the scanning lines,
wherein the drive circuit includes at least one load drive circuit supplied with an input signal having a predetermined voltage amplitude and supplying the driving line with the voltage of the input signal, the load drive circuit comprising:
a differential amplifier circuit having an inverting input terminal, a non-inverting input terminal supplied with a reference voltage and an output terminal connected to the driving line;
a differential voltage holding circuit connected to the inverting input terminal of the differential amplifier circuit and configured to hold a differential voltage between the voltage of the input signal and the reference voltage; and
a first feedback circuit configured to supply the voltage of the input signal to the driving line while a feedback loop including the differential voltage holding circuit is constituted by connecting between the output terminal of the differential amplifier circuit and the differential voltage holding circuit with the differential voltage holding circuit holding the differential voltage.